1. Field of the Invention
The present invention relates generally to an optical disk device and program for recording and reproducing information on and from an optical recording medium such as a compact disk and a digital video disk.
2. Description of the Related Art
As the Internet has remarkably become popularized due to the advance of information and communication technology, much information is actively being exchanged over a network. Under this environment, in the field of information recording device technology, a write-once read-many optical disk, such as a Compact Disk-Recordable (CD-R), or a rewritable optical disk, such as a Compact Disk-Rewritable (CD-RW), is recently attracting attention as a recording medium. Recently, large capacity optical disks, such as a Digital Versatile Disk-Recordable (DVD-R), a DVD-Rewritable (DVD-RW) and a DVD-Random Access Memory (DVD-RAM), are being used for information recording devices, due to the short-wavelength of a semiconductor laser used as a radar light source, a small-sized spot diameter formed by an objective lens having a high Numerical Aperture (NA), and the use of a thin substrate.
When information is provided from a personal computer and recorded on a CD-R, the information is converted into an Eight-to-Fourteen Modulation (EFM) signal and recorded on the CD-R. A difference in the composition of a dye recording layer constituting the optical disk causes a failure in mark forming resulting from the heat accumulation of the recording medium or insufficient cooling speed. For this reason, a desired land or space cannot be formed even though an attempt to record an EFM signal without change is made.
A method of determining a recording parameter intrinsic to each optical disk with respect to a reference recording waveform (hereinafter referred to as a “write strategy”) and maintaining desired recording quality is used.
It is known that the write strategy has a close relationship to recording speed, as do the dye of an optical disk, phase changing material, the thickness of a dye film, or the shape of a groove.
In general, typical write strategies include a method of varying the ratio of pits (marks) to lands (spaces), a method of adding an additional pulse to the front end of a recording pulse, a method of changing the rising or falling position of a pulse using a combination of pits and lands, and a method of making a multi-pulse of a recording pulse.
The method of varying the ratio of pits and lands functions to radiate a short pulse onto an optical disk at high write power and improve the shapes of the front and rear ends of a generated pit by shortening a pit length at the time of low-speed recording.
The method of adding an additional pulse to the front end of a recording pulse functions to improve the shape of a generated pit front end at which it is difficult to convert laser radiation into heat.
The method of changing the rising or falling position of a pulse using a combination of pits and lands can make the distribution of the lengths of formed pits and lands uniform by changing the position of the rear end of a land depending on the length of a previous land because the heat of a previous pit is transmitted to the land and influences a next pit, changing the position of the front end of a recording pit depending on the length of the recording pit because the heat of the recording pit is transmitted forward, changing the position of the rear end of a recording pit depending on the length of the recording pit because the heat of the recording pit is transmitted rearward, or changing the position of the front end of a land depending on the length of a next land because the heat of the next pit is transmitted to and influences the next land.
The method of making a multi-pulse of a recording pulse is a method that is used for a phase-change disk, such as a CD-RW, or a DVD. When information is recorded on the phase-change disk using a continuous pulse, the heat of the phase-change disk itself causes recorded information to be erased from the front end of a pit, so that a multi-pulse having a cooling period between pits is used.
Such a write strategy is optimized and used for each type of optical disk due to the difference in the composition of a dye recording layer constituting the optical disk or the difference in recording speed and, therefore, drive manufacturers require a long period and many processes to optimize the write strategy.
Since there are so many types of commercialized optical disks that drive manufacturers cannot know them all, it is impossible for the drive manufactures to prepare strategies appropriate for all the optical disks on the market.
In order to solve the above problem, a method (for example, Japanese Unexamined Patent Publication No. 2000-30254) of recording information about variant write strategies on a plurality of tracks in the test area of an optical disk and selecting a write strategy that minimizes reproduction jitter, and a method (for example, Japanese Unexamined Patent Publication No. 2003-30837) of recording information using a special recording pattern and acquiring a combination of marks and spaces that minimizes a jitter value or deviation value have been proposed.
However, in the former method, a finally selected write strategy is merely the best of set write strategies, and is not necessarily an optimal write strategy for an optical disk in use. Furthermore, this method is problematic in that only a recording area required for a test occupies the tracks.
In the latter method, since special recording pattern is used, sufficient consideration is not given to an influence on other marks or spaces when a specific mark or space is changed, so that it is difficult to set an optimal write strategy for an optical disk in use using one recording and reproduction test.